Hermetically sealed insulator bushing assembly



April 1, 1952 R. A. SCHOENLAUB HERMETICALLY SEALED INSULATOR BUSHING ASSEMBLY Filed May 15, 1948 INVENTOR. ROBERT A. SCHOENLAUB Patented Apr. 1, 1952 HERMETICALLY SEALED INSULATOR BUSHING ASSEMBLY Robert A. Schoenlaub, Cleveland, Ohio, assignor to Sylvester & Company, Cleveland, Ohio, a

corporation of Ohio Application May 15, 1948, Serial No. 27,258

4 Claims.

This invention relates generally to electrical terminal assemblies and more particularly to hermetically sealed electrical terminal assemblies of the type having composite metal and ceramic structures.

The formation of a satisfactory electrical terminal of the type mentioned above involves many problems, one of which deals with the coefficients of expansion and other properties of the housing, the ceramic insulating element and the electrical connections. Terminals have been provided heretofore, in which tungsten or molybdenum wires have been sealed into a tube with 'a glass having a coefiicient of expansion equal to that of the wires but the problem of sealing steel wires and particularly large ones or massive sections, to steel presents a more difficult problem.

One object of the present invention is to provide an electric terminal assembly of a hermetically sealed type which will be of simple construction and manufactured by a simplified procedure.

Another object is to provide an electric terminal assembly in which a ceramic insulator part is directly sealed to a metallic casing without the use of metal diaphragms or other strain absorbing inserts and without the necessity of welding, soldering or similar processes.

A further object of the invention is to provide a hermetically sealed electric terminal assembly which may be applied during a stressrelieving, brazing or other operation usually necessary during the processing or fabrication of the device to which the terminal assembly is applied.

A still further object is to provide a sealed electric terminal assembly and a method of making the same which will permit the formation of a relatively small seal, 'of for example three eighths of an inch in diameter, which can be placed into a casing composed of a metal of any thickness.

Another object of the invention is to provide a seal in which the ceramic insulator part is formed of stabilized zirconia with or Without supplementary materials to be described later.

Stabilized zirconia is a cubic form of zirconium dioxide containing from 5 to of the oxides of calcium, magnesium, or yttrium in solid solution. Stabilized zirconium oxide has certain unique properties, for example, it has a coefficient of thermal expansion of 1l 10- which is uniform and constant within ranges important to the present invention. 'Also, it can be made to take a glaze, in a manner to be described later, which distinguishes it from magnesia and other high expansion substances which will not take a glaze. To apply the glaze to zirconia, it is necessary that the zirconia body be reasonably dense with a porosity of less than 5% as measured by water absorption, otherwise the plaze will be absorbed to an excessive extent. In obtaining the above mentioned porosity of the zirconia body it is either necessary, due to the high refractory properties, to fire it at about 3300 F. or to bond the zirconia with substances which reduce the maturation temperature to a reasonable degree.

For this purpose it is proposed to use calcium oxide and clay roughly compounded to give the mineral gehlenite (2Ca0.Al2O3.SiO2) in amounts of about 5% of the body. Such bodies fired to 2500 F. for four hours have been found to be satisfactory. Clay may be used alone, but in this case the stabilizing substance may migrate to the bond, giving a body which may crack. This result may be prevented by using a low firing temperature or by using excess stabilizers, such as 8% CaO, in the zirconia. More than 5% clay may be added, using the precaution of either a lime addition or excess stabilizer, or low firing temperatures, or combination of both. In this manner, the coefficient of thermal expansion may be decreased to about 8 10 if it is ever desirable to do so.

Other objects and advantages of the present invention will be apparent from the following 'description, reference being had to the accompanying. drawings wherein a preferred form ofembodiment of the invention is clearlyshown.

Fig. l is a vertical longitudinal sectional view taken through a completed hermetically sealed electric terminal assembly constructed in accordance with the present invention.

Fig. 2 is a vertical sectional view taken through a ceramic insulating bushing used in making the electric terminal assembly shown in Fig. 1.

Fig. 3 is a vertical sectional view taken through the bushing shown in Fig. 2 in the second step of forming a hermetically sealed electric terminal assembly.

Fig. 4 is a similar view showing another step in the formation of the terminal assembly.

Fig. 5 is a vertical sectional view of a spark plug formed in accordance with the present invention.

Figs.'6, 7 and 8 are sectional views of modified forms of sealed terminal assemblies formed in accordance with the present invention.

Referring more particularly to the drawings ,mina, .-;these oxides contribute in some degree to the durability and viscosity, their chief function is and the. composition of the base material. is much less sensitive if the glazing and set- 3 the numeral designates a complete electric terminal assembly constructed in accordance with the present invention. The assembly includes a casing 2| only a portion of which is shown, the casing being, for example, the steel or other metallic housing of a compressor equipped with the terminal assembly. Also included in the assembly is a ceramic bushing 22 which constitutes the insulating element of the assembly. The bushing 22 is preferably formed from stabilized zirconia containing about 8% CaO and 92% ZrOz milled to about 10 microns and mixed with about 5% argillaceous matter (clay, feldspar, silica, sodium silicate, glass, alumina, etc.) This material is dry-pressed, allowing about 7% for shrinkage and fired to an absorption of less than 3%. The bushing is then glazed by dipping or spraying and the metallic connection element 23 is then run through a furnace, with or without a controlled a suitable hole formed in the casing 2|, allowingabout .005" clearance between the refractory part prior to glazing and the metal casing, on all contact edges. If desired, the ceramic piece may be tapered slightly or have a diiferential in the thickness of the glaze to facilitate insertion. The metallic housing is then placed in a furnace, for example, a continuous brazing furnace and fired briefly at 2050 F. When the glaze has softened the bushing with the con-. .nectingelement 23 will settle into final position after which the housing is cooled. The hardening of the glaze will seal the joints between the connection element and the bushing and between the latter and the casing. A nickel dip. may be useful in increasing the adherence ofthe metal to the bushing.

The glaze used must be viscous enough that it will not flow off the bushing or other ele- Iments at the'sealing temperature viz. 2050 F..

Its coeiiicient of expansion must be approxi- .mately equal to that of the metal or slightly less.

It must not contain reducible oxides if used in a reducing atmosphere. It must not dissolve excessive amounts of body material, nor

conduct. electricity, nor be subject to weathering.

One type of glaze which has proven satisfactory for carrying out the present invention may be conveniently considered as consisting of three types of oxides. First it contains acidic oxides such as ,SiOz and B803. These oxides contribute atmospheric durability, high viscosity, and in general the vitreous characteristic, but they reduce the coefficient of expansion and the amounts used therefore, must be limited. Second, it contains amphoteric oxides such as alutitania, beryllia, and zirconia. .While to decrease the solubility of the base substance in the glaze. The alkalies are fluxes, imparting fluidity and high expansion.

' The glaze may be varied in many ways according to the temperature, time of application It t ng temperature is low, than if it is high. It has been found that for a sealing operation at brazing temperatures of the order of 2050 'F.,

a glaze containing from 47 to 57% silica and .boron oxide, from 25 to 35% amphoteric oxides, usually alumina and zirconia, and between 12 and 28% alkali will be satisfactory. It has been found desirable to employ a glaze which has a viscosity at the temperature of insertion of 300 poises or more. The viscosity of the glaze can be controlled to some extent by substituting S102 for B203 and A1203 for ZrOz, but this substitution usually lowers the expansion. The expansion is controlled mainly by varying the alkali content.

In producing a satisfactory glaze, the following combination may be employed:

Parts Frit Zirconium dioxide 20 Ball clay 8 The frit is made from the following batch:

SiOz 318 A1203 NazCOc 382 I-IsBOg 444 In some instances, the process may be varied slightly, for example, the complete assembly may be made during the glazing operation. Fig. 5 shows a spark plug 25 made in this manner. In this spark plug 25 a steel bushing 26 is provided, this bushing having an enlarged wrenchreceiving portion 21, a threaded portion 28 and a cylindrical portion 30 projecting from the threaded portion. The bushing 26 has an axial opening formed therein which is reduced slightly adjacent the upper end of the body to provide a shoulder 3|. A ceramic insulator sleeve 32 of the same or a composition similar to that from which bushing 22 is formed, is disposed in the bushing 26, the insulator 32 hav ing a shoulder 33 to cooperate with the one in the bushing to position the insulator therein. Insulator sleeve 32 receives a metallic electrode 39 which extends through a central opening 34 formed in the sleeve 32 the opening being larger at one end portion to provide an air space between the electrode and the sleeve. When the spark plug 25 is being assembled, the glazing compound is applied to the electrode 39 which is then inserted into the ceramic sleeve. The upper portion of this element is coated with the compound and then inserted into the bushing 26 after which the assembled elements are disposed in a continuous brazing furnace at a temperature of 2050 F. for a suitable length of time such as approximately 20 minutes and then slowly cooled. The fusing of the glaze, its adhesion to the bushing and the metal parts and subsequent hardening upon cooling permanently unites the parts.

The terminal assemblies may be modified in form in many ways. Figs. 6, '7 and 8 illustrate other forms, the one in Fig. 6 having .a plain bushing 34A which is devoid of flanges or shoulders for locating it with relation to the casing body 35. The bushing 34A is formed from the same materials as the bushing 22 and is assembled with the casing 35 and electrode or connection element 35 by the same process'usreception of a plurality of electrodes or connection elements 38. These elements 38 have integral flanges 48 which locate them relative to the body 31 and provide additional surface to effect a better connection.

In Fig. 8 the terminal assembly 4| is of a type formed for removable reception by the easing of an article to be equipped with the assembly. The terminal 41 has a metallic plug-like body 42 provided with a threaded portion in which a counter-bored opening 43 is formed. This opening receives the ceramic insulator element 44 which may be provided with one or a plurality of holes for receiving electrodes 45. The counter boring of opening 43 provides a shoulder 46 which locates the ceramic element 44 relative to the body 42. The same materials and methods of assembly are employed in making the terminal as in the other forms described above.

While several modified forms of seals have been shown and several composition of material for the ceramic insulator and glazehave been described it should be obvious that other modifications in all of these features may be made without departing from the spirit and scope of the invention as set forth in the following claims.

I claim:

1; An electric terminal assembly comprising a metallic casing havin an opening therein; a bushing formed from stabilized zirconia disposed in the opening in said casing; a metallic conductor extending through said bushing into said casing; and a thin coating of glaze between said conductor, said bushing and said casing, said glaze being fused to said elements.

2. A sealed electrical terminal assembly comprising a metallic casing having an opening formed therein; a bushing formed from stabilized zirconia disposed in the opening in said casing; a metallic conductor extending through said bushing into said casing; and a coating of a glaze which is fusible at temperature of the order of 2050" F., on said bushing and the elements adiacent thereto.

3. A sealed electrical terminal assembly comprising a metallic supporting member; a bushing formed from a dielectric material having the same coemcient of expansion as said supporting member; a metallic conductor extending through said bushing; and a coatin on said bushing and the adjacent portions of said supporting member and said conductor, said coating being composed of a glaze which is fusible at a temperature of the order of 2050 F.

4. An electric terminal consisting of a bushing formed from stabilized zirconia; a metal stud extending through said stabilized zirconia bushing; and a film of glaze disposed between and fused to both the bushing and the stud.

ROBERT A. SCI-IOENLAUB.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 653,875 Ochs July 17, 1900 2,138,660 Mann Nov. 29, 1938 2,151,809 Shardlow Mar. 28, 1939 2,210,699 Bahls Aug. 6, 1940 2,241,505 Cuttler Mar. 13, 1941 2,248,644 Reger et al. July 8, 1941 2,279,168 Kalischer et al. Apr. 7, 1942 2,347,187 Frost Apr. 25, 1944 2,434,555 Fischer et al Jan. 13, 1948 2,436,825 Prior Mar. 2, 1948 2,458,748 Stupakofi Jan. 11, 1949 FOREIGN PATENTS Number Country Date 569,282 England May 16, 1945 

